Light emitting sources used in conventional lighting devices may reach high levels of heat intensity. In some circumstances, the heat intensity may be high enough to ignite flammable materials that come into contact with the light emitting source. One such light emitting source is the halogen torchiere bulb.
Typically the halogen torchiere lamp 10 includes a supporting member 12, a housing 14, a bulb 16 and a reflector 18. As illustrated in FIG. 1, the housing 14 includes an upwardly extending U-shaped surface supported by the supporting member 12. The housing 14 supports the bulb 16. Generally, the bulb 16 extends horizontally along the housing 14, and normally has electrical contacts at opposing ends. Each end of the bulb 16 supporting the electrical contacts is received in a socket 24, the socket 24 supporting mating terminal contacts for electrically coupling the bulb 16 to a power source 36, typically, via an on-off switch 38. The socket 24 is coupled to the housing 14 using known techniques such as spot welding or mechanical fasteners.
The housing 14 also supports the reflector 18. In some prior art devices, the housing 14 and the reflector 18 are fabricated as a single unit. If the housing 14 and reflector 18 are separate components, the reflector 18 is positioned in the housing 14 so as to direct the light from the bulb 16 out of the housing 14. Typically a portion of the reflector 18 extends beneath the bulb 16, as illustrated in FIG. 1. Additionally, the housing 14 supports a barrier member or guard 42 that prevents objects from falling into the housing 14 and contacting the bulb 16, shield 40 or reflector 18, and the bulb 16 is covered by a protective shield 40 to prevent inadvertent contact with the bulb 16.
As reported in one news article, halogen bulbs tend to burn much hotter than incandescent and fluorescent bulbs. Halogen bulbs have been known to reach temperatures in excess of approximately 700.degree. F. Consequently, if the halogen bulb comes into contact with cloth, paper or other combustibles, these materials may be ignited.
Many modern designs for the halogen lamp incorporate devices for regulating the operation of the halogen bulb. U.S. Pat. No. 5,733,038 describes one such regulating device. The device includes a sensor mounted on the reflector for generating a sensor light signal corresponding to the light intensity detected by the sensor. The sensor is electrically connected to a control circuit, which interconnects the lamp and a power source. The control circuit is capable of disconnecting the lamp from the power source upon detection that the sensor light signal has reached a level indicative of a condition that the reflector is covered by an object. The disclosed regulator does not measure temperature increases that may occur in the bulb due to malfunction or partial covering.
U.S. Pat. No. 5,801,490 (hereinafter the '490 patent) describes another regulating device. The device disclosed includes a temperature sensor installed on the reflector, near the midpoint of the bulb. The temperature sensor comprises a thermostat electrically coupled to the lamp's electrical circuitry and a half-cylindrical mask. The mask prevents direct illumination of the thermostat body by the bulb, and the thermostat de-energizes the bulb when the sensed ambient temperature reaches a predetermined temperature.
Under certain circumstances, hot spots may develop in the lamp at locations distant from the midpoint of the bulb. This occurrence has been the cause of great concern with respect to potential fire hazards associated with halogen lamps. As a result, the Underwriter's Laboratories, Inc. (UL), a widely recognized, independent, not-for-profit, testing organization, has implemented a safety standard designed to test for hot spots as various points relative to the axis of the bulb.
The "lamp containment barrier" test, Standard 112, becomes effective Jun. 1, 1999. In this test, the lamp is placed in a draft-free room and connected to a variable 120-volt power supply, and adjusted to produce the rated lamp wattage. The lamp is left in the "on" condition for 15 minutes. Without being compressed, a specially prepared cheesecloth pad is placed on top of the lamp so that the cheesecloth is centered along the axis of the bulb. The cheesecloth pad is positioned on the lamp such that the cheesecloth follows the contour of the guard. As a result, the cheesecloth extends over the edges of the guard at both ends, and is as close to the bulb as the lamp's construction permits. The lamp is to be operated until (a) the cheesecloth ignites (flames); (b) a hole develops in any layer of the cheesecloth; or (c) seven hours has elapsed. To successfully pass the test, there shall be no (a) ignition (flaming) of the cheesecloth; or (b) holes developed in any layer of the cheesecloth fabric due to elevated temperatures.
For lamps including an automatic temperature regulating or limiting control, the test is repeated with the cheesecloth positioned at 90 degrees with respect to the axis of the bulb and in any other position that results in a longer time for the control to operate. The test is then repeated with the cheesecloth in the position that resulted in the longest time for the control to operate, with the unit's wattage reduced in 50 watt increments for dimmers that are continuous by changing the input voltage, or selecting a lower step wattage setting for dimmers that are not continuous, until the unit operates for seven hours without operation of the control device.
To satisfy some barrier containment tests, a high temperature limiting sensor capable of detecting localized hot spots that may develop at remote locations along the bulb or within the reflector is needed. There is also a need for a simplified sensor that permits sensing a temperature and de-energizing the lamp without the use of electric sensing components.